Ultrapure water is used in a manufacturing process of products in semiconductor factories, FPD (flat panel display) factories or the like. Among items of water quality for the ultrapure water, there are the number of viable bacteria and the density of TOC (total organic carbon). An ultraviolet sterilization apparatus is employed in the ultrapure water production process as a facility for inactivating microbes, and a low pressure UV oxidation apparatus is employed in the ultrapure water production process as one of facilities for reducing the concentration of TOC. These apparatus provide with one or more low-pressure mercury lamps emitting ultraviolet rays of 254 nm or 185 nm wavelength which are contained in a cylindrical reactor vessel. Each of the lamps is inserted in a lamp-protective tube made of quartz so that the lamp never directly contacts water to be treated or processed in the vessel. The to-be-treated water flows between the outside of the protective tube and the inside of the vessel in a pressurized condition while exposed to ultraviolet rays. Microbes in the to-be-treated water are exposed to the ultraviolet rays of 254 nm wavelength and inactivated thereby. In general, such an exposure is also referred to as sterilization. Further, an OH radical is generated from the to-be-treated water exposed to the ultraviolet rays of 185 nm wavelength, and the TOC is decomposed by oxidation of the generated OH radical to the TOC. Simultaneously, organic substances in the water are directly decomposed by the ultraviolet rays of 254 nm and 185 nm wavelength emitted form the low-pressure mercury lamps. Reactions similar to the aforementioned can be occurred by means of a middle-pressure mercury lamp, a high-pressure mercury lamp, an excimer lamp or the like, not limited to the low-pressure mercury lamp. Quartz, sapphire, fluororesin, etc. are used for a material of the lamp-protective tube.
At least one end of the lamp-protective tube is supported by a wall of the vessel and exposed to the outside so that a lamp can be inserted in and pulled from the lamp-protective tube through the one end exposed to the outside. Further, an elastic sealing member is provided on a portion where the lamp-protective tube is supported in the vessel so that the sealing member adheres to an outer periphery of the lamp-protective tube to seal the inside of the vessel. Typically, the sealing member is an O-ring made of rubber. However, because the ultraviolet rays are irradiated onto not only the to-be-treated water but also the sealing member (O-ring) considerably, accumulation of the irradiation brings the O-ring deterioration due to the ultraviolet rays that causes a possibility of a defect, i.e. water leakage. Particularly, in a case where an output of the low-pressure mercury lamp is increased and quartz having high transmissivity with respect to the 254-nm or 185-nm wavelength is used for the lamp and the lamp-protective tube, the O-ring intends to deteriorate because of the ultraviolet rays within a relatively short period.
It should be noted that there is a known prior art, as indicated in patent literatures listed below, which is constructed to prevent peripheral components from deterioration by light-shielding a part of a light source or a device integrally incorporated in the light source. Patent Literatures 1 and 2 disclose to provide with a ring-shaped UV-shielding member in order to prevent a plastic insulation plug from deterioration due to ultraviolet rays which have leaked through a side of an end portion of a power connection of an arc tube emitting the ultraviolet rays. Patent Literature 3 discloses that, in an ultraviolet treatment apparatus which is configured to emit ultraviolet rays into space from a plurality of UV lamps disposed in parallel with each other and irradiate them to an object to be treated, a UV-shielding membrane is provided on each adjacent side of each of the UV lamps in order to reduce an effect, of the ultraviolet rays emitted from each lamp, to each of adjacent lamps.
Patent Literature 4 discloses that, in a window for an excimer laser, in order to prevent an O-ring for sealing laser medium gas from deterioration due to ultraviolet rays, membranes not transmitting the ultraviolet rays are vapor-deposited on closely-adjacent surfaces of the window and the O-ring, and thereafter, each of the deposited membranes is filmed with an oxidation protective membrane. Patent Literature 5 discloses that, in a solid laser oscillator, in order to prevent an O-ring for liquid-tightly sealing an end of a filter cylinder from deterioration due to excitation rays, a light-shielding ring is provided so as to shield a light leak from an end of an excitation lamp. Patent Literature 6 discloses that, in order to prevent an O-ring for keeping airtightness of a plasma treatment chamber from deterioration, plasma shielding means, which consists of a steel plate in a shape of a thin metallic belt having been wound in a spiral or a conductor wire having been wound in a shape of a solenoid coil or having been netted in a cylindrical shape, is put into a circular groove formed on a side nearer the treatment chamber than another circular groove putting the O-ring thereinto.
However, none of devices disclosed in the aforementioned Patent Literatures is suitable for such a construction as mentioned above that the O-ring is disposed so as to adhere to the outer periphery of the lamp-protective tube. In such a construction, it is necessary for a UV-shielding member to be disposed within the lamp-protective tube. According to the aforementioned Patent Literatures, it is conceivable that the UV-shielding member in a shape of a cylindrical ring is disposed within the lamp-protective tube. In a case where a cylindrical-shaped light-shielding ring is to be employed, it would be ordinary for a skilled engineer to adopt such a construction that employs a light-shielding ring having an outer diameter slightly smaller than an inner diameter of the lamp-protective tube so as to facilitate work for inserting the light-shielding ring into the lamp-protective tube. If so, however, because the light-shielding ring becomes slightly loose in the lamp-protective tube, there would be a problem that, when a UV lamp in the lamp-protective tube should be replaced, the light-shielding ring tends to move because of contact with a base of the UV lamp moving for replacement, so that troublesome correction of a location of the disposed light-shielding ring is required, and that the contact between the light-shielding ring and the base of the UV lamp disturbs a motion of inserting or pulling the lamp. Thus, it is not preferable to dispose the cylindrical-ring-shaped UV-shielding member having a fixed diameter within the lamp-protective tube.